A Research On The Fuzzy Sliding Mode Control Scheme For Static Var Compensator

This paper demonstrates a fuzzy sliding mode control (FSMC) scheme for static VAR compensator (SVC). Strong nonlinearity and changeability of the configuration and operating point are two characteristics of the power system. So it is very difficult to be well controlled. The sliding mode control system is insensitive to the system parameter variations and external disturbances, and it can obtain invariant dynamics and steady-state response in ideal case, so it is feasible to use the sliding mode control for the power system. Now that SVC has been used widely in the power system and some literature states that SVC can not only maintain voltage stability but also effectively improve the power angle stability, the FSMC controller for SVC to improve the power angle stability is designed in this paper.First of all, a nonlinear model for a single-machine infinite-bus system with static VAR compensator is established. Based on the input-output feedback linearization technology, the nonlinear model is converted into a linear model. Then the fuzzy sliding mode control strategy is proposed to improve the power angle stability of the system.The chattering problem is the main obstacle to use the sliding mode control widely. In order to attenuate this phenomenon, the fuzzy logic theory is introduced in the design of the variable structure controller, and a sliding mode variable structure controller is designed which combine the advantages of both fuzzy control and sliding mode variable structure control. In addition, a new fuzzy control by different levels is proposed to improve the performance.Furthermore, the power system is often influenced by disturbance. The disturbance in our system doesn't satisfy the matching condition, so the performance of sliding mode control system is affected by the mismatching disturbance. This paper introduces H∞ robust control theory to design thesliding manifold of the variable structure control system. Thus, another fuzzy sliding mode controller that can attenuate mismatching disturbance is obtained.Finally, The proposed algorithms are verified by simulation using MATLAB/SIMULINK and its toolboxes. The results show that the fuzzy sliding mode controller is rather simple and yet quite efficient, that the power angle stability of the power system is obviously improved by the control system of SVC , and that the advantages of H∞ fuzzy sliding mode control are obvious in comparison with the ordinary fuzzy sliding mode control in attenuating mismatching disturbance and H∞ sliding mode control in reducing chattering.